1. Technical Field
The present invention relates to a recording device attaching a fluid to a medium transported along a transport direction to perform a recording process, a method of generating a correction chart in which marks are formed at a plurality of positions to generate the correction chart in the transport direction of the medium, and a method of transporting a medium in which the medium subjected to the recording process is transported along the transport direction.
2. Related Art
Generally, as a recording device performing a recording process on a medium transported in a transport direction, a recording device alternately repeating a transport process of a sheet as an example of the medium and an attachment process of attaching a fluid to the sheet to perform recording on the sheet is known. A transport device (transport unit) provided in such a recording device is provided with a transport roller disposed further to the upstream side in the transport direction than a recording unit attaching the fluid to the sheet, and a transport motor for applying driving power to the transport roller. At the time of the transport process, the transport motor is controlled to change a rotation position of the transport roller for each set unit angle.
In regard to controlling a transport amount of a sheet, it is preferable that the rotation axis of the transport roller coincide with the center axis of the transport roller. However, in regard to precision in production, it is very difficult for the rotation axis to completely coincide with the center axis. That is, the transport roller is slightly eccentric. For this reason, the transport amount of a sheet (hereinafter, also referred to as “first transport amount”) when the transport roller in which the rotation position is a first position is rotated by a unit angle, and a transport amount of a sheet (hereinafter, also referred to as “second transport amount”) when the transport roller in which the rotation position is a second position is rotated by a unit angle may be different from each other. Such a problem may occur not only when the transport roller is eccentric, but also when an outer circumferential face of the transport roller is deformed by abrasion or the like.
For this reason, in order to reduce the error between the first transport amount and the second transport amount, it is necessary to adjust the rotation amount of the transport roller for each rotation position of the transport roller. From this viewpoint, as a method of correcting the rotation amount of the transport roller at the time of the transport process, that is, the driving amount of the transport motor, a correction method described in JP-A-8-101618 has been proposed.
In the correction method described in JP-A-8-101618, marks are recorded on the sheet transported in the transport direction at a constant interval. Then, a correction chart in which a plurality of marks is formed in the first direction corresponding to the transport direction is generated. In such a correction chart, the interval between marks adjacent to each other along the first direction is an interval corresponding to the degree of the eccentricity of the transport roller. The first transport amount of a sheet when the rotation position of the transport roller is the first position, and the second transport amount of a sheet when the rotation position of the transport roller is the second position are calculated, and correction data based on the calculated rotation positions of the transport roller and the transport amount for each of the rotation positions is generated. At the time of the transport process, the rotation amount of the transport roller is adjusted on the basis of the correction data generated above, to suppress a difference in the transport amount of a sheet for each rotation position of the transport roller.
However, in recent years, development of a recording device provided with a cutting unit to cut a sheet at a cutting position further to the downstream side than a recording unit in the transport direction has proceeded. When a correction chart is generated according to the method described above with such a recording device, the original point position in the circumferential direction of the transport roller is detected, and the driving of the transport roller and the recording unit is controlled to generate the correction chart from the timing when the original point position is detected.
However, when the correction chart is generated by a recording device having the cutting function, a problem represented hereinafter may occur. That is, a discharge unit such as a discharge roller to discharge a part detached from the sheet, to the downstream side in the transport direction is provided on the downstream side of the cutting position in the transport direction of the sheet. At the time of generating the correction chart, the downstream end (hereinafter, also referred to as the “leading end of the sheet”) in the transport direction of the sheet may come in contact with the discharge unit. In this case, a load based on the contact between the leading end of the sheet and the discharge unit is applied to the transport roller (i.e., the transport motor) through the sheet. At this time, the magnitude of the load applied to the transport motor is changed according to the degree of contact between the sheet and the discharge unit. When the magnitude of the load applied to the transport motor is changed during transport of the sheet as described above, the transport amount of the sheet may be changed also according to the change of the load. For this reason, when the correction chart is generated, it is necessary to make position in the transport direction of the leading end of the sheet constant at the generation start point.
As an example of a method of accurately adjusting the position of the leading end of the sheet, a method is conceivable in which the absolute position type encoder to detect the absolute position in the rotation direction of the transport roller is provided, and the rotation position of the transport roller is adjusted such that the leading end of the sheet at the time of generating the correction chart is located at a predetermined position. In this case, since it is possible to prevent the load applied to the transport motor from being changed whenever the correction chart is generated, it is possible to stabilize and generate the correction chart. However, the absolute position type encoder is very expensive, and there is a problem that the recording device becomes expensive.
To “stabilize and generate the correction chart” means that it is possible to generate a correction chart equivalent to the previous correction chart if the shape of the outer circumferential face of the transport roller is not changed from the time the previous correction chart was generated.